Posteromedial corner

 

Key structures of the 'neglected corner' of the knee

The key passive restraints of the posteromedial corner are the -

• superficial medial collateral ligament
• deep medial collateral ligament
• posterior oblique ligament

The key dynamic restraint is the semimembranosus expansion (SME) - the expansion of the semimembranosus tendon, inserting on the femur, tibia and the medial meniscus. 

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Instabilities from PMC injury

Disruption of the PMC can cause anteromedial rotational instability. Usually injury of the PMC occurs in association with anterior or posterior cruciate ligament tears. The key issue is that cruciate reconstructions may fail if the surgeon does not recognise and address the PMC instability.

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Diagnosing injury to the posteromedial corner

Clinical examination should include valgus stress testing - supporting the lower leg at the ankle while testing the 'give' when pushing the knee inwards. The dial test and anteromedial drawer tests examine for laxity in rotation.

MRI should support the clinical examination initially if the medial collateral ligament is ruptured. Valgus stress X-rays may be useful in the assessment of more chronic injuries.

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Management of posteromedial corner injuries

Isolated partial ruptures of the superficial medial collateral ligament are usually treated conservatively with a range-of-motion brace.

Indications for operating on acute injuries include -

• both tibial and femoral bony avulsions, where the ligaments have been ripped loose from their bony attachments together with a piece of the bone
• intra-articular entrapment, where damaged soft tissue gets caught up in the joint
• a “Stener lesion” where soft tissue gets sandwiched in the wrong place and prevents the MCL from re-attaching to the tibia bone

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Forum discussions

• Re: Any footballers torn their ACL AND MCL?

  Footballers getting to grips with the issues around MCL injury.

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Peer-reviewed papers

• Quote:

  "Injury [to the posteromedial corner] is common and compromise of the medial restraints may result in the development of valgus and rotatory laxities, increased forces on the cruciate ligaments or persistent pain and dysfunction....[and] determining which higher-grade PMC injuries warrant surgical repair or reconstruction can be challenging...."

  Citation: Chahla J, Kunze KN, LaPrade RF, Getgood A, Cohen M, Gelber P, Barenius B, Pujol N, Leyes M, Akoto R, Fritsch B, Margheritini F, Rips L, Kautzner J, Duthon V, Togninalli D, Giacamo Z, Graveleau N, Zaffagnini S, Engbretsen L, Lind M, Maestu R, Von Bormann R, Brown C, Villascusa S, Monllau JC, Ferrer G, Menetrey J, Hantes M, Parker D, Lording T, Samuelsson K, Weiler A, Uchida S, Frosch KH, Robinson J. The posteromedial corner of the knee: an international expert consensus statement on diagnosis, classification, treatment, and rehabilitation. Knee Surg Sports Traumatol Arthrosc. 2021 Sep;29(9):2976-2986. doi: 10.1007/s00167-020-06336-3. Epub 2020 Oct 26. PMID: 33104867; PMCID: PMC7586411.

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